This invention relates to the fabrication of the semiconductor devices and more particularly to the separation of semiconductor wafers into device chips. Wafer separation is a well developed art and involves various mechanical techniques including scribing and breaking, as well as various sawing methods. More recently laser cutting has also been utilized. Certain types of devices require processes of photoresist masking and chemical etching to satisfactorily divide the wafer with its plurality of device chips into individual devices. There are, of course, combinations of the foregoing techniques, for example, a combination of scribing or sawing and chemical etching may be used.
However, certain semiconductor devices, particularly those in which the chip must be intimately connected over a relatively large area to the mounting base in order to provide good thermal conductance, require a relatively heavy coating of gold or gold alloy on the back surface of the chip to enable a eutectic bond to be made at a relatively low temperature. It is impractical to attempt to provide the metal plating at a stage other than in the large wafer form. However, pure gold and useful gold alloys are difficult to penetrate cleanly because of their relative softness and ductility. At least one effort of the prior art involves a series of treatments to first embrittle a gold plating to enable chip separation by conventional means followed by a treatment to reproduce the original state of ductility. This technique as well as other expedients obviously introduce additional process steps which are disadvantageous, particularly those that involve heating operations.
Accordingly, an object of this invention is a method of separating semiconductor wafers having relatively heavy gold or gold alloy platings into device chips by conventional means by the addition of a simple processing step not involving heat treatment or other deleterious effect.